Lead-acid batteries are known and have achieved wide acceptance in a variety of fields.
Valve-regulated lead-acid batteries, particularly so-called absorbent glass mat or xe2x80x9cAGMxe2x80x9d valve-regulated lead-acid batteries have achieved significant acceptance in recent years as sources of standby electrical power. These absorbent glass mat valve-regulated lead-acid batteries have become widely used to provide standby power for telecommunications applications, typically for cellular telephone towers, other telecommunications equipment and computers. In such applications, the absorbent glass mat valve-regulated lead-acid batteries are maintained on a standby basis; power is drawn from these absorbent glass mat valve-regulated lead-acid batteries only when the primary source of power to the cellular telephone towers, other telecommunications equipment or computer is interrupted, such as during a failure of a public utility power grid. In such instance, the absorbent glass mat valve-regulated lead-acid batteries, which may have been on standby for a number of years, supply power until the primary source of power, typically the public utility grid, has returned to service.
Gas recombination catalysts have been used in flooded lead-acid batteries as well as in other battery systems. These catalysts have been positioned externally to the battery cells contacting the open atmosphere. The catalysts recombine oxygen and hydrogen gas on their surfaces, converting the gas back into water vapor which condenses and flows back into the battery. Such catalysts have found limited application in standby batteries and have not been used heretofore for valve-regulated lead-acid batteries due to the need for compact, space efficient installation which is inconsistent with having an external catalyst unit.
Valve-regulated lead-acid batteries designed for standby service typically are electrolyte-limited, having the entire electrolyte absorbed in microfibrous glass mat material serving as the separator between the positive and negative plates. Any water loss from the battery reduces total water volume available and increases concentration and specific gravity of the sulfuric acid electrolyte. Loss of liquid volume can lead to partial loss of contact between the absorbent glass mat separator and the active plates within the battery, resulting in premature performance degradation.
It has been found that absorbent glass mat valve-regulated lead-acid batteries in standby, back-up power service, tend to lose capacity over time, even if a small trickle charge of current is applied automatically to the battery. It has also been found that catalysts, notably palladium, when positioned in intimate contact with vapor phase electrolyte in an absorbent glass mat valve-regulated lead-acid battery, tend to stem such capacity losses by enhancing the reaction by which hydrogen and oxygen recombine into water within the cell; it is this recombination reaction which gives such cells their xe2x80x9crecombinantxe2x80x9d name. Reduction in loss of capacity and consequent greater confidence in the ability of such cells to provide standby power over a long term, such as for twenty years, has been attributed to the catalyst recombination of hydrogen and oxygen into water and thereby reducing loss of hydrogen and oxygen gas with the attendant loss of potential for generation of water from the cell.
This invention is based on the surprising and unexpected discovery that multiple cells in a standby service valve regulated recombinant lead-acid battery placed in vapor communication one with another may be served by a number of catalyst units fewer than the number of cells with excellent performance. Such batteries exhibit substantially better gassing rates than conventional non-catalyst equipped batteries with conventional (non-vapor communicating) cells and have significant manufacturing advantages.
The catalyst units are desirably associated with vent valve housings, positioned just below the pressure relief vent. As a result, gas trying to escape from head space via which multiple cells vapor communicate one with another is in proximity with the catalyst unit.
Surprisingly, in such batteries even in standby service, there is sufficient mass transfer among vapor-communicating cells that oxygen and hydrogen gas produced by the electrolytic reaction recombine under the effect of the catalyst even though the catalyst is not in immediate proximity with some of the vapor-communicating cells. When batteries embodying the invention are on float, there is a considerable decrease in gas escaping when a catalyst is provided in a common head space, reducing and in some cases effectively eliminating water loss. Additionally, decreases in float current have been observed in batteries embodying the invention vis-a-vis comparable non-catalyst equipped commercially available batteries. Moreover, there is an improvement in retention of electrical performance in batteries embodying the invention vis-a-vis comparable commercially available batteries without the catalyst. Water vapor produced through the electrolytic reaction apparently does not concentrate in the vicinity of the catalyst but distributes itself throughout common head space shared by multiple vapor-communicating cells.
In one of its aspects this invention provides a recombinant lead-acid battery including a case, a plurality of lead-acid cells within the case, where each cell includes a plurality of positive and negative lead metal plates, and absorbent separator material between at least some of the positive and negative plates. In this aspect of the invention, the case preferably includes partitions for separating adjacent cells one from another with portions of the partitions being spaced from the proximate portion of the case to define space for mass transfer vapor migration and partial pressure equalization among the cells within the case. At least one catalyst unit is preferably connected to the case and communicates with the mass transfer vapor migration and partial pressure equalization space to enhance recombination of hydrogen and oxygen into water within the battery.
The catalyst unit is preferably constructed together with a vent valve for the battery so as to be removable from the battery unitarily with the vent valve for ease of maintenance and manufacture. The catalyst material preferably sits in a cage connected to a lower portion of the vent valve so that upon insertion of the vent valve into the battery case, the catalyst material enters the vapor communication space via which mass transfer vapor migration and partial pressure equalization occurs among a plurality of cells within the battery.
The catalyst unit is desirably at least partially within the battery case and is most preferably essentially if not totally within the battery case. The catalyst is preferably palladium or a palladium alloy, most preferably 0.5 percent (0.5%) palladium deposited on alumina or carbon. Other suitable catalysts include platinum, ruthenium, rhodium, other metals of the platinum group, precious metals, other noble metals and compounds such as tungsten carbide. While the preferred loading of the catalyst on the substrate is 0.5 percent (0.5%), 0.8 percent (0.8%) also works well and loadings of one percent (1%) or less are the preferred range. However, catalyst loadings may be as high as ten percent (10%) by weight of the substrate.
In another of its aspects, this invention provides a recombinant lead-acid battery which includes a case and a plurality of lead-acid cells within the case where each cell includes positive and negative lead metal plates and absorbent separator material between some of the positive and negative plates. Some or all of the cells within the case are in vapor mass transfer and partial pressure equalization communication one with another. A plurality of catalyst units are in vapor communication with the cells and enhance recombination of hydrogen and oxygen into water within the battery, with the plurality of catalyst units preferably being fewer in number than the plurality of lead-acid cells. Preferably at least some of the catalyst units are at least partially within the battery case and most preferably at least some of the catalyst units are completely within the battery case. The catalyst units are preferably constructed to be essentially integral with a vent valve for the battery which is removable from and replaceable in the battery case. Most preferably, the vent valve/catalyst unit combination fits into the top of the battery case, at a position at which gasses evolving during the electrolytic reaction would collect.
In yet another of its aspects, this invention provides a method for operating a recombinant lead-acid battery having a case, a plurality of lead-acid cells within the case, with each cell including positive and negative lead metal plates, and absorbent separator material between at least some of the positive and negative plates, where the method comprises placing at least some of the cells into vapor communication one with another and placing a plurality of discrete catalyst units fewer in number than the vapor communicating cells into vapor communication with the cells to enhance recombination of hydrogen and oxygen into vapor phase water within the battery.
In another of its aspects, this invention provides a pancake-style recombinant lead-acid battery having a case with vertically stacked pluralities of lead-acid cells within the case. Each cell preferably comprises a plurality of horizontal positive and negative lead metal plates and absorbent separator material between at least some of the positive and negative plates. Pluralities of-cells are in vapor communication one with another. The battery further includes catalyst units connected to the case and communicating with spaces via which cells of respective pluralities vapor communicate one with another, for enhancing combination of hydrogen and oxygen within the battery. The number of catalyst units is preferably less than the plurality of cells. Respective catalyst units are preferably provided connected to the case and communicating with respective cell vapor communication spaces on a one-to-one basis. The pancake-style recombinant lead-acid battery manifesting aspects of the invention may include terminals, for connecting the battery to a load, which exit from a vertical external surface of the case or from a horizontal external surface of the case. In the pancake configuration, one or more common head spaces may be provided at the top of the battery with suitable passageways provided for communication therewith by the pancaked plates and separators. In another configuration of the pancake-style recombinant battery, the catalyst units and, optionally, a vent-valve plug constructed integrally therewith, may be provided at the side of the battery with suitable internal configurations permitting vapor communication from the plates to the catalyst unit/vent plug combinations.
The battery preferably further includes partitions within the case for separating adjacent cells one from another with portions of the partitions being spaced from the case to define the cell vapor communication space.
The partitions preferably include vertical and horizontal partitions with some of the partitions being spaced from the case interior to define the cell vapor communication space. The horizontal partitions may block vapor communication between vertically stacked cells in the pancake-style recombinant lead-acid battery manifesting aspects of the invention.
In yet another of its aspects, this invention embraces a lead-acid battery having a case comprising a jar and a cover and a plurality of lead-acid cells within the jar. Each cell preferably includes a plurality of upstanding positive and negative lead metal plates and absorbent separator materials between at least some of the positive and negative plates. The jar preferably includes upstanding partitions for separating adjacent cells one from another with upper portions of the partitions being spaced from the cover to define space for vapor migration among cells. A catalyst unit is preferably connected to the case and communicates with the vapor migration space to enhance recombination of hydrogen and oxygen into water in at least partially vapor phase within the battery.
In this aspect of the invention, plates of a given plurality of respective cells may having upstanding terminal tab portions extending above the upper portions of the partitions. In such case, the battery may further include electrically conductive members connectively extending between the terminal tab portions of plates of like plurality of adjacent cells. The electrically conductive members are preferably lead-metal strips and are preferably welded to respective terminal tab portions.
As a variation, the jar may have upstanding partition portions for separating adjacent cells one from another and the cover may include downwardly extending partition portions aligned with the upstanding partition portions to define partitions which, with walls of the case, form compartments for the cells. The partitions may have apertures therethrough for vapor communication among cells in respective compartments. Upper portions of the plates may be spaced from the cover to define space for vapor residence. At least one catalyst unit is preferably connected to the case and communicates with a vapor residence space for enhancing recombination of hydrogen and oxygen into water within the battery. The number of catalyst units are preferably less than the plurality of cells.
In yet another variation, portions of the partitions which are spaced from the cover may be aligned and form the upper parts of the partitions proximate to the cover. The spaced portions may be cutouts formed in upper parts of the partitions proximate to the cover and may be longitudinally aligned. The cutouts may be rectangular and may be formed in upper edges of the partitions. The cutouts are preferably completely above the plates of the cells but may be only partially above the plates of the cells.